In recent years, various types of flat panel display devices have been developed. Although different display devices have different light emitting theories, electrodes are arranged in all kinds of display devices, and light emission is controlled by applying voltage between the electrodes. For example, in FED (Field Emission Display), electrons released from the field emitter are supplied to a phosphor to emit light. When light emission is controlled by turning on/off said electrodes, a dielectric (insulator) is arranged around each electrode for various purposes. For example, an insulating material is arranged between the electroconductive parts in order to insulate the area between the electroconductive parts. Insulating material is also arranged to partition electrodes.
Even if a dielectric and insulator have the same composition, they are sometimes are called a “dielectric” and sometimes called an “insulator”, depending upon the position and purpose of the arrangement. Consequently, the insulating material arranged around the electrode is called “dielectric” hereinafter. However, the technical range hereinafter is not limited by the method of use. The “dielectric” mentioned in the technology described below includes both “dielectrics” and “insulators”.
Glass powder and inorganic filler can be used as the dielectric material. Pattern printing or etching methods using photoresist can be used to form the dielectric pattern. However, it is difficult to form fine pattern by means of pattern printing. In the etching method using photoresist, the etching object is usually limited to a thin film. Since the insulating material arranged between electroconductive parts must be a thick film, the etching method using photoresist is inappropriate for this application. In order to form a thick film as the insulating material, a technology using a photosensitive insulator thick film paste to form a fine pattern was developed.
Examples of insulator paste include glass paste and inorganic filler paste. When manufacturing a display device (for example a flat panel display), a glass substrate is used almost exclusively as the base substrate, and the firing temperature is limited to be 600° C. or lower, preferably, 550° C. or lower. In this case, if an inorganic filler is contained in the paste, sintering will be restrained, making it difficult to obtain a compact dielectric. Consequently, it is preferred to use glass paste mainly composed of glass when manufacturing a display device. Under this premise, the following technology is identified which uses a photosensitive insulator paste to form fine patterns.
Japanese Kokai Patent Application No. Hei 8[1996]-50811 discloses a photosensitive glass paste for use in a plasma display panel, containing glass powder, an acrylic copolymer containing carboxyl groups and ethylenic unsaturated groups in the side chain or at the molecular terminal, a photoreactive compound, and a photopolymerization initiator. When this photosensitive insulating glass paste is used to form a dielectric pattern, first, the glass paste is coated on a substrate, followed by drying to evaporate the solvent. Then, a photomask is used to expose a prescribed pattern. As a result of exposure, the organic photosensitive binder in the exposed part is crosslinked and polymerized, but not developed. The unexposed part is developed by means of alkali development to obtain a non-sintered dielectric in the desired pattern. After that, it is sintered at a desired temperature to obtain a dielectric. However, Japanese Kokai Patent Application No. Hei 8[1996]-50811 does not disclose a thick film type dielectric with good adhesivity to a desired base nor does it disclose a dielectric with very good insulation properties.
Japanese Kokai Patent Application No. 2004-318116 discloses a glass powder type photosensitive paste, which is a photosensitive paste containing fine oxide particles with particle size in the range of 0.005-0.08 μm, inorganic particles other than fine oxide particles, and a photosensitive organic component, and has the average refractive index N1 of the fine oxide particles and the organic component and the average refractive index N2 of the inorganic particles other than the fine oxide particles satisfying the following formula:−0.07≦N2−N1≦0.07(N2>1.65)However, this reference does not disclose any thick film type dielectrics with good adhesivity to a desired base and very good insulation property. Also, lead-containing glass has been used as the aforementioned glass powder type photosensitive paste. As consciousness of environmental protection is being raised on the global scale, using lead-type glass should be avoided as much as possible. On the other hand, it is difficult to find equal or better characteristics (for example, said adhesivity and/or insulation property) compared with those of dielectrics manufactured using lead-type glass.
The purpose of the present invention is to provide a thick-film type dielectric with good adhesivity to a desired base (for example, substrate) and very good insulation properties. Also, preferably, the purpose of the present invention is to provide an environment-friendly lead-free type dielectric.